The present invention relates to compound archery bows, and particularly to a device to aid in replacing a bowstring and for retaining tension in the cables of a compound bow as the bowstring is being replaced and while the compound bow is stored without a bowstring installed.
A compound bow is an archery bow such as the one disclosed in Allen U.S. Pat. No. 3,486,495. A compound bow includes cables which ride on eccentric pulleys mounted on the bow limbs, enabling such a bow to impart a greater amount of energy to an arrow than was previously possible using simple archery bows. Because of these cables and pulleys, the limbs of a compound bow flex through a smaller distance as the bow is drawn fully than do the limbs of a simple bow. However, in order to store the energy of the drawn bow, the limbs of the compound bow are much stiffer than those of a simple bow, and are very difficult to bend manually.
Optimum performance of a compound bow requires that the bow be tuned, so that the eccentric pulleys rotate in proper relationship to one another, and so that the two limbs of the bow each do the proper amount of work in propelling an arrow. Tuning the compound bow may include adjustment of the length of each of the cables, one of which is associated with each limb of the bow, by adjusting the amount of each cable which is wound upon a respective cable adjustment drum. Some compound bows also require adjustment of the positions of the limbs with respect to the central frame portion of the bow. Once a compound bow has been properly tuned, it is important to maintain some tension on the cables at all times, since relaxing tension could allow one of the cables to shift on the adjustment drum, slightly changing the effective length of that cable and disturbing the tuning of the bow.
A compound bow usually has a replaceable fiber bowstring. The bowstring is normally attached by a loop at each of its ends to a hook or other bowstring fastener which is usually swaged onto the end of one of the two cables of the compound bow. Through use, the fiber bowstring eventually becomes worn and must be replaced with a new one. So long as a new bowstring is of identical length to the old bowstring, and tension is maintained on the cables during replacement of the bowstring, no retuning of the bow is necessary upon replacement of the bowstring.
Since shooting a bow is an acquired skill, and depends upon predictable response of the bow, it is important that an archer in the field should be able to quickly and easily change bowstrings without altering the performance of the bow. It is therefore desirable for a bowstring changing device to be easily carried for use in the field by a bow hunter.
It is also desirable to store a compound bow with its bowstring tension relaxed, so that the limbs do notaquire a "set". If a compound bow is unstrung and the cables are allowed to become slack, however, the bow will need to be retuned when it is restrung.
Devices enabling replacement of a bowstring without disturbing the tuning of the bow have been disclosed in Carlson U.S. Pat. No. 4,050,137 and Smith U.S. Pat. No. 4,074,409. While both the Carlson device and the Smith device enable a bowstring of a compound bow to be replaced without necessitating retuning the compound bow, neither of these devices is particularly easy to use.
The Carlson device comprises a steel cable having a slotted tubular engagement member fixed at each end of the cable. One engagement member may be slipped over each cable of the bow while the bowstring is installed. Tension must then be taken on the cable of the Carlson device, as, for example, by drawing the cable in a fashion similar to that used to draw the bow using the bowstring, to relieve tension in the bowstring. The bowstring must then be replaced while tension is held in the cable of the bowstring changing device. Because compound bows are often very strong and stiff, it becomes awkward and difficult for one person alone to both pull the Carlson bowstring changer cable and simultaneously remove or replace the bowstring. While the Carlson device is simply constructed, its steel cable makes it bulky and cumbersome to carry in the field.
The Smith device uses a nylon cord to interconnect a pair of hooks, each resembling a pair of curved fingers with a slot therebetween, used to engage the bowstring fastener on each cable. The nylon cord is looped around a pulley fastened to one of the hooks, and a simple friction device is used to control the separation between the hooks so long as tension is maintained in the nylon cord. While the Smith device allows the user to easily replace a bowstring once sufficient tension is applied to slacken the bowstring, it is possible to inadvertently dislodge the hooks from the cables of the compound bow while applying tension to the Smith device. Additionally, the Smith device requires the user to manually pull the ends of the bow limbs toward one another, a difficult task with a strong compound bow.
What is needed, therefore, is an easily and securely installed and easily operated device for replacing the bowstring of a compound bow. Such a device should be capable of being carried easily for use in the field. It should also be usable for storing a compound bow in a partially relaxed condition with the bowstring removed, without loss of tuning of the compound bow, and without danger of the device becoming dislodged from the cables of the compound bow.